Known opto-electronic devices are based on use of Group XIII element(s) nitrides such as AlN, GaN and InN and mixed Group XIII element nitrides containing two or three Group XIII elements. Such nitrides have thus far been commercially manufactured on sapphire or silicon-carbide substrates, differing in nature and structure from the thereafter deposited nitride layers (heteroepitaxy) using such methods as MOCVD, HVPE, MBE and others.
Numerous attempts have thus far been made to develop other methods for obtaining bulk mono-crystalline Group XIII element(s) nitride, in particular bulk mono-crystalline gallium nitride and reported in the number of papers and disclosed in various patents or patent applications.
Bulk mono-crystals of gallium-containing nitrides have recently been obtained form the supercritical ammonia-containing solution of soluble precursors of such nitrides by selective crystallization on crystallization seeds as described in WO 02/101120. Further improvements in the proposed technology have been reported in WO 03/035945.
In the environment of supercritical ammonia-containing solution a dynamic equilibrium between fluid and solid phase can be achieved and controlled so that relatively thick layers of desired gallium-containing nitrides can be deposited on the seeds.
It has been proven in the course of further studies on the process parameters, that the growth rate, purity, crystalline quality and surface quality of the bulk mono-crystalline Group XIII element(s) nitride(s) depend on a number of factors and can be easily distorted by inadequate control of the process parameters.
Surprisingly, it has been discovered that the results achieved in terms of growth rate and quality of the product depend also on the composition of the supercritical ammonia-containing solution, in particular on the composition and concentration of a mineralizer used as a component of such a solution.
Thus, it is a main object of the present invention to provide an improved process for obtaining bulk mono-crystalline gallium-containing nitride(s) suitable for commercial exploitation, in which the product obtained thereby can have desired, properly balanced crystalline and surface properties.
It is also the aim of the present invention to provide means for control of solubility of the starting material used as a feedstock containing Group XIII element(s), in particular gallium.
Still further aim of the invention is to provide means for control of growth rate of Group XIII element(s) nitride mono-crystals, while ensuring the required quality of the obtained crystals, enabling use of the same in various opto-electronic devices. In this aspect of the invention elimination of oxygen impurities is of a particular importance.